The most common cause for this to occur is that the pipe between the pump and pressure bottle have become porous and the water being pumped just leaks back to the well. The only solution is to replace the pipe. The replacement pipe should be plastic lined.
Your well pump is constantly running? How old the pump is? location? Only two things comes to mind. The underground water level is low, or the sensor is not working correctly. Get the installer to service the equipment
Bad check valve,foot valve,holding tank.First check the holding tank ,pump runs ,fills the holding tank, pump shuts off,tank should have 60 psi and hold pressure, if pressure starts to decrease with out faucets on see the the above. install a check valve before the holding tank